Dotsafe will offer participating schools filtering technology for life, as well as personalized e-mail accounts for every student, a school Web page and the guarantee that there will be no advertising on portal pages.

CNN: Filtered ISP offers free service to schools nationwide

But a survey carried out by mail filtering firm CipherTrust has shown that spammers are the most enthusiastic users of the SPF technology.

BBC: NEWS | Technology | Spammers exploit anti-spam trap